A majority of the energy used to provide fuels today is derived from fossil fuels, despite much effort and research on various alternative energy or non-fossil fuel options. The utilization of renewable biomass to produce fuel has been promoted by various governments, including the United States government through the Energy Independence and Security Act (“EISA”) of 2007. Some of the purposes of the act are to increase the production of clean renewable fuels, to promote research on and deploy greenhouse gas (“GHG”) capture and to reduce fossil fuels present in fuels. Notably, the act sets out a Renewable Fuels Standard (“RFS”) with increasing annual targets for the renewable content of fuel sold or introduced into commerce in the United States.
The mandated annual targets of renewable content in fuel are implemented through an RFS that uses tradable credits (called Renewable Identification Numbers, referred to herein as “RINs”) to track and manage the production, distribution and use of renewable fuels for transportation or other purposes. RINs can be likened to a currency used by obligated parties to certify compliance with mandated renewable fuel volumes. The U.S. Environmental Protection Agency (“EPA”) is responsible for overseeing and enforcing blending mandates and developing regulations for the generation, trading and retirement of RINs.
Many approaches have been developed to use renewable biomass to produce transportation fuel or biofuels. Commercial biofuel production from carbohydrates currently employs starch or sugar cane as the feedstock. Production of ethanol from corn starch is widespread and ethanol from this source is considered a renewable fuel, and a first generation biofuel. It is often blended with gasoline, for example at levels of approximately 10% and the resulting blended gasoline can be considered to be a partially renewable transportation fuel. A given volume of such ethanol can have a RIN associated with it. This RIN is transferable to buyers of the ethanol or to producers of finished transportation fuel who use the ethanol to manufacture their finished transportation fuel.
However, starch and sugar cane are in high market demand as a food source for humans and animals, put upward pressure on food costs and thus are expensive and undesirable feedstocks for biofuel production. By contrast, agricultural residues and other non-food waste are inexpensive due to their wide availability and limited market value, and do not put pressure on food costs. Consequently, non-food feedstocks offer an attractive alternative to the starch and sugar cane feedstocks used to date as a source for biofuel production.
One of the leading approaches to producing liquid fuel from renewable feedstock involves the conversion of cellulosic biomass, a non-food source, to simple alcohols, such as ethanol, butanol and methanol. These alcohols can be used in a mixture with gasoline, or in their pure form, as liquid transportation fuel. Much attention and effort has been applied in recent years to the production of such liquid fuels from cellulosic biomass.
Cellulosic ethanol, in particular, has been the subject of significant research efforts. One of the leading technologies for producing ethanol from cellulosic biomass involves subjecting agricultural waste or other feedstocks containing cellulose to a series of chemical and biological treatments to produce glucose, which is then fermented to produce the ethanol. In particular, the process includes a chemical and/or heat pretreatment to improve the accessibility of the cellulose contained in the feedstock. This is followed by an enzymatic hydrolysis with cellulase enzymes to convert the cellulose to glucose. The glucose is fermented to ethanol by microorganisms, optionally in the presence of other sugars derived from the feedstock.
Other research efforts have been devoted to methanol and isobutanol production. One approach for producing methanol includes a thermochemical treatment of a feedstock to produce syngas, which is composed of hydrogen and carbon monoxide. The syngas is subsequently converted into the methanol, or other alcohols, with the aid of a chemical catalyst. Further research efforts have been directed to isobutanol production from renewable feedstocks by fermentation with yeast genetically engineered for such purpose.
Research and development efforts have also been directed towards the production of oils and diesels from renewable biomass. One technology includes a biomass catalytic cracking process that employs heat and a catalyst to convert biomass to a renewable crude oil with a relatively low oxygen content. Further, microorganisms have been used to ferment feedstock into carboxylic acids, which are then neutralized to form carboxylate salts. The carboxylate salts are then dewatered, dried and thermally converted to ketones, which are subsequently hydrogenated to form alcohols that can be refined into diesel or other fuels. Furthermore, oil can be produced from microalgae, which can then be converted to renewable diesel for ships or jet fuel. Moreover, other groups are investigating the production of biodiesel by yeast fermentation of feedstocks to an isoprenoid, which in turn is converted to diesel by a multi-step finishing process.
Other research efforts have been directed towards the production of gaseous hydrogen for direct use as a transportation fuel, which can be used in an internal combustion engine or a fuel cell. Such hydrogen can be produced by a variety of techniques. Some of the processes described in the literature include biomass pyrolysis or gasification and biological processes, such as bacterial fermentation and enzymatic hydrogen production.
At present, however, there is limited technical and economic infrastructure to support the widespread use of hydrogen directly as a transportation fuel. Although much effort has been devoted to using the gas as a transportation fuel, hydrogen is highly volatile and thus is dangerous to store and transport.
Yet another approach to generate a gaseous renewable fuel from waste feedstock includes anaerobic digestion of organic material derived from plants, vegetation, municipal waste, animal waste, animal byproducts, manure, sewage sludge, food waste, food processing waste, agricultural residues including corn stover and wheat straw and/or other biomass, hereinafter referred to collectively as “waste organic material”. The combustible product of this digestion is referred to herein as “biogas” which may be produced by anaerobic digestion of any waste organic material. A main constituent of biogas is methane, although the gas also contains carbon dioxide and other components, depending on its source. The biogas may be produced by decomposing waste organic material under anaerobic conditions, such as in landfills.
There are commercial biogas applications that use biogas to produce electricity. In farming operations, biogas has been used to fuel engine-generators to produce electricity for on-farm use. In landfill operations, projects are underway to use biogas for electricity generation, either for on-site use or to sell to the grid. Other uses of biogas that have been described include transmitting biogas via pipeline to be combusted by an end user to fuel boilers, dryers, kilns, greenhouses, and other thermal applications (see http://www.epa.gov/statelocalclimate/documents/pdf/7.4_landfill_methane_utilization.pdf)
Furthermore, in developing countries biogas is used for cooking.
The commercialization of processes for using biogas as a fuel has met limited success despite research and development efforts in this area. Although conventional gasoline powered automobiles can be run on biogas, they need to be retrofitted with compressed natural gas cylinders, which take up significant space in the trunk of a car or the bed of a pickup truck. To overcome the storage problems, automobiles need to be specially manufactured to accommodate the tanks under the body of the vehicle. Moreover, infrastructure required for biogas refueling is both costly and complex to implement and the demand for methane-fueled automobiles is relatively low. Thus, refueling stations are not always plentiful or conveniently located.
Although there have been numerous and wide ranging research efforts devoted to the implementation of renewable fuel production, the existing technologies for producing transportation or heating fuels with renewable content have been difficult to commercialize for various reasons. Despite business and legislative efforts to promote the production of renewable transportation or heating fuels, little progress has been made. There is therefore a need for a process that allows the energy in biomass to be captured and used in transportation fuel for conventional automobiles. Furthermore, there is a need to commercialize the use of biomass and other renewable resources as a source of energy, particularly for transportation or heating fuel. Technology that produces transportation or heating fuel from non-food biomass waste in a cost-effective manner would be desirable.